WO-A-02/42715 describes a method for analyzing the surface of a glazing unit consisting of extracting, by digital processing for each pixel of the digitized image, local phases in two directions. Variations of local phases make it possible to calculate variations of local slopes of the surface of the glazing so as to deduce therefrom variations in the curvature or variations in the height of the surface.
It is possible, by comparing variations in the curvature of the glazing with reference quantities, to proceed to a choice as to whether to reject the glazing.
Nevertheless, although this possible selection criterion certainly makes it possible to judge the curvature of the glazing it does not necessarily make it possible to judge the esthetic quality of the image produced in reflection by the glazing. In point of fact, according to the position of the observer, a surface defect will not have the same effect on the image in reflection.
If an attempt is made to use such a method for judging the esthetic quality of the glazing in reflection, some glazing units would sometimes be rejected without, for all that, being really prejudicial esthetically or vice versa.
Moreover, with a method of this type, the calculated quantities on the edges of the glazing are not generally reliable.
Finally, this type of method requires long and difficult calibration.
WO-A-2007/115621 and U.S. Pat. No. 6,392,754 also describe methods aimed at measuring the shape of the surface of the glazing. These methods notably have the same disadvantage as regards the relevance of the assessment of the esthetic quality of the glazing.